From: Arno Wagner <arno@wagner.name>
To: dm-crypt@saout.de
Subject: Re: [dm-crypt] length of keyfiles
Date: Wed, 6 Jan 2021 11:47:46 +0100 [thread overview]
Message-ID: <20210106104746.GA3386@tansi.org> (raw)
In-Reply-To: <b2f9f2aa1134d54b1d08cabfb275e0bc@kngnt.org>
Hi Felix,
I assume we are talking LUKS here, plain mode is different.
The longer length is both convenience and helps if you
use low-entropy input. The keyfile does not actually
hold a key (LUKS mode), but a passphrase. Passphrases
get hashed, and once you have maximum entropy, you
cannot get more. I would need to look up what length
is actually used, but it does not depend on the lenght
of the encryption key. That one is stored in the anti-forensic
stripes, protected with the hash from that passphrase.
So, to make this short, if you use LUKS with a keyfile,
putting in more entropy than used is meaningless.
If your random data is from /dev/random or (properly
initialized) /dev/urandom, 64 bytes are more than enough.
Also, the differences between an 8kB passphrase and a
64B one in execution time should not be noticeable at all.
Unless you read it from floppy disk ;-)
Regards,
Arno
On Wed, Jan 06, 2021 at 10:17:22 CET, Felix Rubio wrote:
> Hi everybody,
>
> I have seen that keyfiles can be used in cryptsetup up to 8 kB, but
> internally the master key is 512 bits at max. Is there any recommendation
> / increased security by using a random sequence of 8 kB w.r.t., let's say,
> one of just 64 bytes?
>
> I understand that using one of 8kB will require more time than one of 64 B
> when unlocking the volume, but... is the former really that much more
> secure than the latter?
>
> Regards!
> Felix
> _______________________________________________
> dm-crypt mailing list
> dm-crypt@saout.de
> https://www.saout.de/mailman/listinfo/dm-crypt
--
Arno Wagner, Dr. sc. techn., Dipl. Inform., Email: arno@wagner.name
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next prev parent reply other threads:[~2021-01-06 10:48 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-06 9:17 [dm-crypt] length of keyfiles Felix Rubio
2021-01-06 10:47 ` Arno Wagner [this message]
2021-01-06 11:08 ` Felix Rubio
2021-01-06 11:17 ` Felix Rubio
2021-01-06 14:06 ` Arno Wagner
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